Japanese Knotweed – signs to look out for
Japanese Knotweed is an invasive species initially brought across from Japan in the 1800s. Since then, its remarkable ability to spread through rhizome growth meant people used it in all sorts of applications, such as along railway lines and in manor gardens.
Once the British people (and those from other countries it was taken) realised its threat, it was too late. Now, we have to live with this plant. It’s generally harmless until it comes into contact with buildings and the surrounding areas. That’s when the problems start.
Until recently, the presence of Japanese Knotweed meant real difficulties with buying and selling a home. However, Government legislation and RICS guideline changes mean that provided a remediation plan is in place, it’s not a deal-breaker.
Nevertheless, Japanese Knotweed is essential to watch out for. Here are a few of the signs.
Signs of Japanese Knotweed in spring
After lying dormant through spring, the first warmer days bring about buds and shoots. Look for dark red or green shears that resemble asparagus or a little bamboo plant. The spade-shaped leaves will be dark red or green when they first emerge.
The zig-zag bamboo-like structure is easiest to see at this time, without too many leaves and flowers blocking your view. If you cut the plant back at the base, you’ll notice an orange root – these are the rhizomes.
Japanese Knotweed grows at an extraordinary rate in late spring and early summer. The canes should up, sometimes reaching around three metres in just one season. At the same time, the leaves turn a normal shade of green.
Signs of Japanese Knotweed in summer
By the middle of summer, Japanese Knotweed will have reached its full height for this year. It could be well over 2 metres high if it’s not been trimmed.
At this stage, you can snap the stems with your hand easily. They’ll still have that dark red colour, but the leaves will have turned green with potential red/purple splotches.
Right at the end of summer, Japanese Knotweed flowers. You’ll see creamy white blossoms appear among the dense foliage.
Signs of Japanese Knotweed in autumn
The leaves turn a bright yellow in autumn, and the seed casings are shed onto the ground. Don’t worry too much about these – the nature of how Japanese Knotweed grows means they’re extremely unlikely to result in new plants. The rhizomes are a much bigger problem.
As the leaves drop, the stems turn brown. If they aren’t cut back, they’ll go a straw-like colour as you head into winter. They’ll remain here, and while they appear dead, the plant is very much alive. It’s simply dormant, ready to return in spring.
Can you spot Japanese Knotweed in winter?
You can spot Japanese Knotweed in winter if the plant isn’t cut back. The dark brown or straw-coloured stems resemble bamboo. If you check the roots (rhizomes) underneath, they’ll be easy to snap with your hand and be brown/orange inside.
There are also reports that climate change means Japanese Knotweed is budding earlier. The milder winters make growing conditions optimal earlier than usual, so you might see buds emerging as early as March.
What to do if your home survey finds Japanese Knotweed
If you or your home survey finds Japanese Knotweed, there’s one very crucial first step: don’t panic.
This situation is likely treatable, and although these procedures can be pretty expensive, they’re not too costly in relation to a house.
In fact, Japanese Knotweed might even put a lot of the competition off when buying, leading to a lower price.
The thing with Japanese Knotweed is that you need to completely eliminate all traces of the rhizomes. If even a tiny amount remains, the plant will grow back.
The two most common ways to treat Japanese Knotweed are excavation and chemical treatment (a glyphosate-based herbicide). Allow up to £5,000 for one of these jobs, although hopefully, they won’t cost this much.
GB Home Surveys is a team of chartered surveyors. Our RICS-registered teams work in the South-West, West Midlands and South Wales.
To learn more about how one of our home surveys can help you identify Japanese Knotweed, feel free to get in touch with us. Use the contact form below to reach out for an obligation-free, friendly chat. We’ll get back to you as soon as possible.
